Most commercial alkaline batteries are primary use, meaning that after a single discharge they are disposed of and replaced. Primary alkaline batteries are produced in high-volume at low-cost by numerous commercial manufacturers. Non-rechargeable, or primary batteries, such as alkaline and carbon-zinc types, make up 80% of dry-cell batteries sold each year. While primary batteries may cost less initially, the need to replace them more frequently than rechargables (which can be used tens to hundreds of times) ends up costing more. Alkaline batteries contain manganese dioxide, graphite, steel, and zinc. Because the cost of recycling non-rechargeable batteries exceeds the value of the materials that can be recovered, fees must be charged to make recycling them economically feasible. Unfortunately, many primary batteries still end up in landfills in spite of community and government efforts.
Each year, over 3 billion primary household batteries are purchased in the United States. Many of these contain heavy metals, such as cadmium, lead, lithium, mercury, nickel, silver, and zinc. If improperly disposed of, buried in landfills, or incinerated, these batteries can harm the environment by leaching into surface water or groundwater, or escaping into the air and soil.
Rechargeable alkaline batteries have recently come to market based on technology developed by Battery Technologies Inc. (See, for example, U.S. Pat. No. 4,957,827, U.S. Pat. No. 5,204,195, U.S. Pat. No. 5,281,497, U.S. Pat. No. 5,336,571, U.S. Pat. No. 5,340,666, U.S. Pat. No. 5,346,783, and U.S. Pat. No. 5,424,145). The technology was commercialized by Pure Energy, Grandcell, EnviroCell, and Rayovac among others. Nonetheless, battery cycle life in rechargeable alkaline batteries is limited due, in part, to the high depth of discharge that is used in commercial applications, which causes irreversible change to the electrochemical components of the battery. Furthermore, manufacturers make proprietary chargers for use with their rechargeable alkaline batteries, which are meant to improve cycleability (See, for example, U.S. Pat. No. 4,977,364, U.S. Pat. No. 8,153,300, and U.S. Pat. No. 7,718,305), and are offered only in small form factors. In general, consumers can expect their rechargeable alkaline batteries to last for tens of cycles to a couple hundred cycles. These limitations have prevented rechargeable alkaline batteries from achieving mainstream adoption; the market for household batteries is still dominated by primary batteries.
Currently, manufacturers recommend against recharging primary batteries because of the danger of acid leaks, fires, and explosions. But, if a way could be found to recharge primary batteries safely and inexpensively, they could be used again and again, thus reducing the amount of batteries in need of recycling.
There is a long-felt need to establish optimum operational parameters for alkaline batteries, both secondary and primary, which achieve maximum cycle life. It would be especially useful to be able to control battery operating discharge conditions, in addition to charge conditions, in order to prevent the irreversible changes that are caused by over-discharging.